Black phosphorus integrated tilted fiber grating for ultrasensitive heavy metal sensing

We propose an integrated black phosphorus (BP)-tilted fiber grating (TFG) configuration as an enhanced light-matter interaction platform for heavy metal chemical sensing. We synthesized BP nanosheets by using a liquid-phase exfoliation method and developed an in-situ layer-by-layer (i-LbL) technique for BP nanosheets deposition. These approaches secured high-quality BP coating on specific fiber cylindrical surface with strong adhesion as well as a prospective thickness control. By taking advantage of i-LbL deposition, the unique optical tunable features including coating thickness-dependent polarization and polarization- selective coupling have been experimentally observed. Furthermore, the BP-TFG was exploited as the first BP-fiber optic chemical sensor for heavy metal Pb2+ ions detection, demonstrating significant performance of ultrahigh sensitivity up to 0.5 × 10−3 dB/ppb, much lower limit of detection down to 0.25 ppb, and extremely wide concentration range from 0.1 ppb to 1.5 × 107 ppb. We believe that this BP-fiber optic architecture opens the path as an optical platform for superior chemical sensing and biomedical applications